1. Field of the Invention
The present invention relates to an optical scanning apparatus and a scanning image display apparatus having the same. In particular, the present invention is suitably used to cases where a surface to be scanned is two-dimensionally scanned with a light beam by deflecting means so that a two-dimensional image is to be viewed on the surface to be scanned.
2. Description of the Related Art
There has been known a two-dimensional optical scanning apparatus that performs optical scanning by deflecting a light beam emitted from light source means two-dimensionally using deflecting means and focusing the beam as a spot on a surface to be scanned using an optical system.
There has been proposed a scanning image display apparatus in which a two-dimensional image is to be viewed as residual image of a scanning locus on a surface to be scanned in two dimensional scanning with a deflected light beam (see U.S. Pat. No. 5,485,225).
The deflecting means used for deflecting a light beam from light source means includes a polygon mirror, a Galvano mirror, and a MEMS device manufactured using MEMS (Micro Electro-Mechanical Systems) technology.
The deflecting means performs fast scan in a first direction by changing the deflection direction fast and slow scan in a direction perpendicular to the first direction by changing the deflection direction slowly. In the two-dimensional optical scanning apparatus, each scanning line is formed through fast scan by the deflecting means, and scanning lines are arranged sequentially side by side by slow scan, whereby a two dimensional scan image is formed on a surface to be scanned.
The scanning line refers to a light scanning locus in scanning the surface to be scanned with light in the first direction (i.e. the direction in which the scanning speed is faster).
In the case where an image is projected onto a screen from an oblique direction, a keystone distortion occurs in the image displayed on the screen, as is well known.
The following methods have been proposed as methods for correcting keystone distortion in projected images.
In one proposed method, some pixels in a horizontal line of an image signal are removed or thinned out to make an image displayed on a liquid crystal panel (i.e. a projection screen on which an image is projected) inverted-trapezoidal to cancel a keystone distortion that is generated when the image is projected, thereby displaying a rectangular image on the projection screen (see Japanese Patent Application Laid-Open No. H08-009306).
In another known method, light emission control means for preventing a light source from emitting light corresponding to predetermined pixels so that the number of pixels displayed in a unit area in a rectangular image display area becomes uniform, whereby keystone distortion of the projected image is corrected and a rectangular image is displayed (see Japanese Patent Application Laid-Open No. 2000-180779).
It is also known that non-linearity distortion also occurs in projected images. In still another known method, an image signal is thinned out in such a way as to cancel a distortion in the vertical direction to correct non-linearity distortion (see Japanese Patent Application Laid-Open No. H08-079669).
In the image projection apparatus disclosed in U.S. Pat. No. 5,485,225, a laser beam is two-dimensionally deflected by two deflectors in the forms of a multi face mirror and a swivel mirror so that a two dimensional scan image is formed on a screen. However, this document does not refer to keystone distortion or non-linearity distortion of the two-dimensional scan image.
In the projection image display apparatus using a liquid crystal panel disclosed in Japanese Patent Application Laid-open No. H08-009306, the number of pixels in the image projected on the screen decreases toward the upper side, and therefore the resolution of the projected image is not uniform.
In the two-dimensional scanning projector disclosed in Japanese Patent Application Laid-open No. 2000-180779, keystone distortion in the projected image is corrected by allowing emission of light from the light source only in the portion corresponding to the rectangular image display area defined to conform with the shortest scanning line. Accordingly, the number of pixels in one scanning line in the image projected on the screen decreases toward the upper side, and therefore the resolution of the projected image is not uniform.
In the liquid crystal display disclosed in Japanese Patent Application Laid-Open No. H08-079669, keystone distortion is corrected by thinning-out or superimposition of image signal performed according to the position in the vertical direction. Accordingly, the number of pixels along the vertical direction in the image projected on the screen decreases toward the upper side, and therefore the resolution of the projected image is not uniform.